Lehman Ronald A, Kuklo Timothy R
Department of Orthopaedic Surgery and Rehabilitation, Walter Reed Army Medical Center, Washington, DC 20307, USA.
Spine (Phila Pa 1976). 2003 Sep 15;28(18):2072-7. doi: 10.1097/01.BRS.0000084628.37133.BA.
A biomechanical study of cadaver vertebrae to determine the feasibility of obtaining adequate thoracic pedicle screw fixation in a salvage situation. OBJECTIVE To investigate the ability to safely place a thoracic pedicle screw with adequate maximal insertional torque (MIT) using the anatomic trajectory (AT) (directed along the true anatomic axis of the pedicle) after purposeful failure/medial violation of the pedicle using the straight-forward trajectory (ST) (paralleling the vertebral endplate).
Failure to place a pedicle screw at an intended segment of the thoracic spine may theoretically render the level uninstrumented, because pedicle hook placement may be unsafe and the transverse process may be fractured. An alternative pedicle screw insertion technique, if biomechanically sound in this situation, may present an excellent alternative for critical instrumentation levels.
Fixed-head 5.0 mm stainless steel pedicle screws were placed using the ST and MIT was recorded after determination of bone mineral density (BMD) with dual-energy radiograph absorptiometry (DEXA) scanning. Purposeful screw malposition and critical pedicle wall failure were performed, followed by salvage placement of the screw using the AT. Insertional torque was recorded for each screw revolution with a digital torque wrench and MIT was again recorded to compare the MIT obtainable in the salvage situation.
BMD for the vertebrae averaged 732 g/cm2 (620-884 g/cm2). The MIT for the straight-forward technique without pedicle violation was 2.61 +/- 0.19 (SE) inches per pound, whereas that of the salvage procedure after medial wall violation (AT) averaged 1.62 +/- 0.12 (SE) inches per pound. Therefore, the AT achieved 62% (P = 0.027) of the fixation strength (in terms of MIT) during salvage after failure/medial violation of the pedicle. MIT for both the ST* and AT trajectories correlated with both global BMD of the vertebrae (*P = 0.008; P = 0.004) and regional BMD of the vertebral body (*P = 0.044; P = 0.023).
The AT achieved 62% (P = 0.027) of the MIT during salvage of a failed/violated pedicle. BMD correlated with both the initial and salvage techniques. The AT provides adequate fixation in a salvage situation and may be safely used to provide segmental fixation at critical levels.
一项对尸体椎骨的生物力学研究，以确定在挽救情况下获得足够的胸椎椎弓根螺钉固定的可行性。目的是研究在使用直入轨迹（ST）（平行于椎体终板）有意破坏/内侧侵犯椎弓根后，沿着解剖轨迹（AT）（沿着椎弓根的真正解剖轴方向）安全置入胸椎椎弓根螺钉并获得足够最大插入扭矩（MIT）的能力。
在胸椎预期节段未能置入椎弓根螺钉理论上可能导致该节段未被器械固定，因为置入椎弓根钩可能不安全且横突可能骨折。如果在这种情况下生物力学上合理，一种替代的椎弓根螺钉置入技术可能为关键的器械固定节段提供极佳的选择。
使用ST置入5.0毫米固定头不锈钢椎弓根螺钉，在用双能X线吸收法（DEXA）扫描测定骨密度（BMD）后记录MIT。有意造成螺钉位置不当和关键椎弓根壁破坏，随后使用AT挽救性置入螺钉。用数字扭矩扳手记录每个螺钉旋转时的插入扭矩，并再次记录MIT以比较在挽救情况下可获得的MIT。
椎骨的BMD平均为732克/平方厘米（620 - 884克/平方厘米）。未侵犯椎弓根的直入技术的MIT为2.61±0.19（标准误）英寸磅，而内侧壁侵犯后（AT）的挽救操作的MIT平均为1.62±0.12（标准误）英寸磅。因此，在椎弓根失败/内侧侵犯后的挽救过程中，AT达到了固定强度（就MIT而言）的62%（P = 0.027）。ST和AT轨迹的MIT均与椎骨的整体BMD（*P = 0.008；P = 0.004）和椎体的局部BMD（*P = 0.044；P = 0.023）相关。
在失败/侵犯的椎弓根挽救过程中，AT达到了MIT的62%（P = 0.027）。BMD与初始技术和挽救技术均相关。AT在挽救情况下提供了足够的固定，可安全用于在关键节段提供节段性固定。
